In existing miniature handheld devices such as cell phones, PDAs, and MP3 players dedicated analog ICs are almost exclusively used to control switch mode power supplies (SMPS). The ICs consume very low power and, usually, operate as constant frequency pulse-width modulator (PWM) controllers that are, because of less wide-bandwidth noise, preferred to variable-frequency solutions. The analog controllers require relatively long design process and need to be almost completely redesigned each time implementation technology changes. As such, they are not suitable for monolithic integration with fast changing digital hardware, on which the majority of portable devices are based. Moreover, in the latest CMOS processes not all functional blocks of analog controllers can be implemented due to very limited supply voltages.
Digital control of low-power SMPS allows easier system integration and, supported by automated design tools, fast transition of designs from one implementation technology to another. Furthermore, the digital control can simplify realization of advanced power management techniques.
Although the potentials of digital controllers are known, in low-power SMPS they are sporadically used. Implemented in the same IC design technology, the digital controllers take significantly larger silicon area, have higher power consumption, and, often operate at lower switching frequency that result in poor efficiency and a larger power stage that negate all digital advantages.